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Geohazards questions and answers

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A summary of questions and answers from the Geohazards field trip:

If there was a major event involving the Kermadec Trench, what affect would this have?

Hi Jasmine, The Kermadec Trench is a subduction zone. There could be earthquakes causing limited shaking in New Zealand. These earthquakes may cause tsunami which could reach New Zealand. There are submarine volcanoes too. 
From volcanologist Sam Hampton.

Are there hydrothermal eruptions in New Zealand? If there are, where are they most likely to occur? 

Hi Te Ana, the North Island has volcanic regions especially around Taupo and Rotorua and out to White Island. Hydrothermal eruptions are steam driven eruptions. White Island had a hydrothermal eruption last month. Rotorua in 2006 near the hospital - 150m high from a 20m wide pond with no warning. Hydrothermal eruptions often occur without warning.
From Sam Hampton.

What inspired you to study geohazards and why do you think people should follow in your tracks? In your opinion what is the most interesting geohazard and why?

Hi Sebastian, Ali says he is from the UK where there are few geohazards. He finds them interesting and wonders about helping people when geohazards occur. He was interested in volcanoes first. I got into geology as I could get out in the landscape and see the processes and effects on people. Volcanoes are my favourite. Currently I am looking at mitigtaing the effects of ashfall on roofs.
From Sam Hampton.

What is it like working around geohazards and what are you researching right now about geohazards? 

Hi Lily, I am looking at how geohazards affect infrastructure like roads, electricity, water, sewage, internet and the mobile phone network. I go out in the field a lot and in my office I use GIS software a bit like Google Earth to do analysis.
From Alistair Davies.

What will happen if the Alpine Fault line ruptures? How much damage would this cause?

Hi Alexander, it could be large (magnitude 8.0) which will likely set off landslides which can then cause flooding which may affect things directly such as damaging a building. Indirect affects are where it might damage a road so people cannot use it which will indirectly lead to a reduction in tourism. In the short term there will be a lot of damage but longer term people may not want to visit eg tourists.
From Alistair Davies.

Here in Whitianga what is the biggest tsunami we could get if there happened to be one? Is it possible that an earthquake like the Christchurch earthquakes could happen here in Whitianga? 

Hi Thomas, I’m not a tsunami expert but GNS and other scientists are trying to assess the risk of tsunami in New Zealand. For example, the risk of proximal (close to home earthquakes) comes from fault lines close to the coast and there would not be much warning for these tsunami. Subduction zones like the Kermadecs are further away so there would be some warning while earthquakes in places like South America could affect New Zealand’s East Coast but there would be hours of warning. Geonet and GNS web sites are good sources of information. Scientists didn’t know about the faults under Christchurch. In Coromandel, mining has helped to gain knowledge about faults there. In your area there are different fault mechanisms from in the Christchurch system.
From Sam Hampton. 

Will the next Alpine Fault earthquake be more serious than the Christchurch earthquake?

Many people are predicting a magnitude 8 earthquake when the Alpine Fault next ruptures. Christchurch and New Zealand are now better prepared for earthquakes. An Alpine Fault rupture may trigger landslides and flooding especially on the West Coast which could be cut off for a while and hard to it will be hard to support them. Less people live close to the Alpine Fault but the shaking could cause widespread damage.
From Alistair Davies.

Will anything happen to the sea, when the Alpine Fault earthquake strikes? 

Most effects will be on the land. If the rupture extends south of the South Island then it could  cause tsunami. Milford Sound has steep cliffs around the fiords and these could produce large landslides that displace water in the fiords causing tsunami.
From Alistair Davies

Will Methven feel the Alpine Fault earthquake and what will happen?

Yes you will feel a lot of shaking from a full rupture producing a magnitide 8 earthquake with a possible 3 minutes of shaking. It will make it hard to stand and furniture will move.
From Sam Hampton.

Why is it that on average in New Zealand every ‘150-200 years’ a major earthquake happens?

"Major" is more like every 20-30 years in New Zealand. High magnitude that is far away will not have a big effect. Christchurch 2011 was more damaging than 2010 as it was right under the city and shallow.
From Alistair Davies.

How long ago did the last major earthquake happen along the Alpine Fault and when can we expect the next one?

The last one was 1717 and was a full rupture so along most of the fault broke. Every 300-400 years magnitude 7.9 to 8.3 earthquakes can be expected. Scientists say there is a 30% chance of it rupturing in the next 50 years.
From Sam Hampton.

Do you know what geohazards might affect the Kerikeri area? 

The main hazard is a tsunami from the Kermadecs, which has happened before. The Taupo Volcanic Zone can have huge eruptions where ash could reach Kerikeri.
From Sam Hampton.

Are there any underwater volcanoes around New Zealand?

Hi Joe, there are lots of extinct volcanoes. Active volcanoes are found in an area from White Island to the Kermadecs and there are lots of active volcanoes here - some above and some below sea. NIWA have imaged them as part of their research.
From Sam Hampton.

Where is a tsunami most likely to occur in New Zealand?

Hi Lauren, yes the likelihood is important to consider but all New Zealand’s coastline is exposed to tsunami and everyone needs to prepare.
From Sam Hampton.

What is the most common geohazard in New Zealand? 

Hi Marshall, landslides are probably the most common - caused by high rainfall. Lots of flooding often goes with it. We have lots of small earthquakes too.
From Alistair Davies.

How big an area can be affected by earthquakes? 

Hi Kiriwai, it depends how big it is. Small faults cause small earthquakes and affect small areas. Magnitude 8 over a long fault will shake the whole of the South Island and be felt as far away as the North Island and east coast of Australia.
From Sam Hampton.

My class are keen to know what sort of shaking we could expect here in Hokitika?

Some severe shaking, buildings will be damaged and liquefaction around rivers and low lying river plains is possible. A major Alpine Fault rupture could cause a 300-400km long rupture so will have a big effect.
From Sam Hampton.